From Wikipedia, the free encyclopedia

An offshore platform, often referred to as an
oil platform or an oil rig, is a
large structure used to house workers and machinery needed to drill
wells in the ocean bed, extract oil and/or natural gas, process the produced fluids,
and ship or pipe them to shore. Depending on the circumstances, the
platform may be fixed to the ocean floor, may consist of an
artificial
island, or may float.

Most offshore platforms are located on the continental
shelf, though with advances in technology and increasing crude
oil prices, drilling and production in deeper waters has become
both feasible and economically viable. A typical platform may have
around thirty wellheads located on the platform and directional drilling allows
reservoirs to be accessed at both different depths and at remote
positions up to 5 miles (8 kilometers) from the platform.

Remote subsea wells may also be connected to a
platform by flow lines and by umbilical connections; these subsea
solutions may consist of single wells or of a manifold centre for
multiple wells.

History

Around 1891 the first submerged oil wells were drilled from
platforms built on piles in the fresh waters of the Grand Lake St. Marys (a.k.a. Mercer County
Reservoir) in Ohio. The wide but
shallow reservoir was built from 1837 to 1845 to provide water to
the Miami and Erie Canal.

Around 1896 the first submerged oil wells in salt water were
drilled in the portion of the Summerland field extending under
the Santa Barbara Channel in California. The wells
were drilled from piers extending from land out into the
channel.

In early 1947 Superior Oil erected a drilling/production
platform in 20 ft of water some 18 miles off Vermilion Parish,
Louisiana. But it was Kerr-McGee Oil Industries (now Anadarko Petroleum
Corporation), as operator for partners Phillips Petroleum (ConocoPhillips)
and Stanolind Oil & Gas (BP), that
completed its historic Ship Shoal Block 32 well in October 1947,
months before Superior actually drilled a discovery from their
Vermilion platform farther offshore. In any case, that made
Kerr-McGee's well the first oil discovery drilled out of sight of
land.

The Thames Sea
Forts of World War
II are considered the direct predecessors of modern offshore
platforms. Having been pre-constructed in a very short time, they
were then floated to their location and placed on the shallow
bottom of the Thames estuary.[1][2]

Types

Larger lake- and sea-based offshore platforms and drilling rigs are
some of the largest moveable man-made structures in the world.
There are several distinct types[3]
of platforms and rigs:

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Fixed
platforms

These platforms are built on concrete and/or steel legs anchored directly onto the seabed,
supporting a deck with space for drilling rigs, production
facilities and crew quarters. Such platforms are, by virtue of
their immobility, designed for very long term use (for instance the
Hibernia platform). Various types of
structure are used, steel jacket, concrete caisson, floating steel and even
floating concrete. Steel
jackets are vertical sections made of tubular steel members, and
are usually piled into the seabed. Concrete caisson
structures, pioneered by the Condeep concept, often have in-built oil
storage in tanks below the sea surface and these tanks were often
used as a flotation capability, allowing them to be built close to
shore (Norwegianfjords and Scottishfirths are popular because they are sheltered and
deep enough) and then floated to their final position where they
are sunk to the seabed. Fixed platforms are economically feasible
for installation in water depths up to about 1,700 feet (520
m).

Compliant
towers

These platforms consist of slender flexible towers and a pile
foundation supporting a conventional deck for drilling and
production operations. Compliant towers are designed to sustain
significant lateral deflections and forces, and are typically used
in water depths ranging from 1,500 to 3,000 ft (450 to 900
m).

Semi-submersible
platform

These platforms have hulls (columns and pontoons) of sufficient
buoyancy to cause the
structure to float, but of weight sufficient to keep the structure
upright. Semi-submersible platforms can be moved from place to
place; can be ballasted up or down by altering the amount of
flooding in buoyancy tanks; they are generally anchored by
combinations of chain, wire rope and/or polyester rope during
drilling and/or production operations, though they can also be kept
in place by the use of dynamic positioning.
Semi-submersibles can be used in water depths from 200 to 10,000
feet (60 to 3,050 m).

Jack-up
platforms

Jack-up platforms (or jack-ups), as the name suggests, are
platforms that can be jacked up above the sea using legs that can
be lowered, much like jacks. These platforms are typically used
in water depths up to 400 feet (120 m), although some
designs can go to 550 feet (170 m) depth. They are
designed to move from place to place, and then anchor themselves by
deploying the legs to the ocean bottom using a rack and pinion
gear system on each leg.

Drillships

A drillship is a maritime vessel that has been fitted with
drilling apparatus. It is most often used for exploratory drilling
of new oil or gas wells in deep water but can also be used for
scientific drilling. Early versions were built on a modified tanker
hull, but purpose-built designs are used today. Most drillships are
outfitted with a dynamic positioning system to
maintain position over the well. They can drill in water depths up
to 12,000 feet (3,660 m).

Floating production
systems

The main types of floating production systems are FPSO (floating
production, storage, and offloading system). FPSOs consist of
large monohull structures, generally (but not always) shipshaped,
equipped with processing facilities. These platforms are moored to
a location for extended periods, and do not actually drill for oil
or gas. Some variants of these applications, called FSO (floating storage and offloading
system) or FSU (floating storage unit), are used exclusively
for storage purposes, and host very little process equipment.

Tension-leg
platform

TLPs are floating platforms tethered to the seabed in a manner
that eliminates most vertical movement of the structure. TLPs are
used in water depths up to about 6,000 feet (2,000 m). The
"conventional" TLP is a 4-column design which looks similar to a
semisubmersible. Proprietary versions include the Seastar and MOSES
mini TLPs; they are relatively low cost, used in water depths
between 600 and 4,300 feet (200 and 1,300 m). Mini TLPs can also be
used as utility, satellite or early production platforms for larger
deepwater discoveries.

Spar
platforms

Spars are moored to the seabed like TLPs, but whereas a TLP has
vertical tension tethers, a spar has more conventional catenary
mooring lines. Spars have to-date been designed in three
configurations: the "conventional" one-piece cylindrical hull, the
"truss spar" where the midsection is composed of truss elements
connecting the upper buoyant hull (called a hard tank) with the
bottom soft tank containing permanent ballast, and the "cell spar"
which is built from multiple vertical cylinders. The spar has more
inherent stability than a TLP since it has a large counterweight at
the bottom and does not depend on the mooring to hold it upright.
It also has the ability, by adjusting the mooring line tensions
(using chain-jacks attached to the mooring lines), to move
horizontally and to position itself over wells at some distance
from the main platform location. The first production spar was Kerr-McGee's Neptune, anchored in 1,930
feet (588 m) in the Gulf of Mexico; however, spars (such as Brent Spar) were
previously used as FSOs. Eni's Devil's Tower is located
in 5,610 feet (1,710 m) of water, in the Gulf of Mexico, and is
currently the world's deepest spar; however, when Shell's Perdido spar is installed
(expected mid-2009), it will be the deepest at almost 8,000 feet
(2,438 m). The first Truss spars were Kerr-McGee's Boomvang and
Nansen. The first (and only) cell spar is Kerr-McGee's Red
Hawk.

Normally Unmanned
Installations (or NUI)

These installations (sometimes called toadstools), are small
platforms, consisting of little more than a well bay, helipad and emergency shelter. They are
designed to operate remotely under normal conditions, only to be
visited occasionally for routine maintenance or well
work.

Conductor Support
Systems

These installations, also known as satellite
platforms, are small unmanned platforms consisting of
little more than a well
bay, and a small process plant. They are designed to operate
in conjunction with a static production platform which is connected
to the platform by flow lines and/or by Umbilical cable.

Particularly large
examples

The Hibernia
platform is the world's largest (in terms of weight) offshore
platform, located on the Jeanne D'Arc basin, in the Atlantic Ocean
off the coast of Newfoundland. This Gravity base Structure
(GBS), which sits on the ocean floor, is 364 feet (111 m)
high and has storage capacity for 1.3 million barrels
(210,000 m3) of crude oil in its 278.8-foot
(85.0 m) high caisson. The platform acts as a small concrete
island with serrated outer edges designed to withstand the impact
of an iceberg. The GBS
contains production storage tanks and the remainder of the void
space is filled with ballast with the entire structure weighing in
at 1.2 million tons.

Maintenance and supply

A typical oil production platform is self-sufficient in energy
and water needs, housing electrical generation, water desalinators
and all of the equipment necessary to process oil and gas such that
it can be either delivered directly onshore by pipeline or to a
floating storage unit and/or tanker loading facility. Elements in
the oil/gas production process include wellhead, production manifold, production separator, glycol process to dry gas,
gas
compressors, water injection pumps,
oil/gas export metering and main oil line pumps.

Larger platforms are assisted by smaller ESVs (emergency support
vessels) like the BritishIolair that are summoned when something has gone
wrong, e.g. when a search and rescue operation is
required. During normal operations, PSVs (platform supply vessels)
keep the platforms provisioned and supplied, and AHTS vessels can also
supply them, as well as tow them to location and serve as standby
rescue and firefighting vessels.

Crew

Essential
personnel

Not all of the following personnel are present on every
platform. On smaller platforms, one worker can perform a number of
different jobs. The following also are not names officially
recognized in the industry.

Drawbacks

Risks

A typical offshore Oil/Gas platform.

The nature of their operation — extraction of volatile
substances sometimes under extreme pressure in a hostile
environment — means risk, accidents, and tragedies occasionally
occur. In July 1988, 167 people died when Occidental Petroleum's Piper Alpha offshore
production platform, on the Piper field in the UK sector of the North Sea, exploded after a
gas leak. The resulting investigation conducted by Lord Cullen, and
was called the 'Cullen Report', was highly critical of a number of
areas, including, but not limited to, management within the
company, the design of the structure, and the Permit to Work
System. The report was commissioned in 1988, and was delivered
November 1990.[4] The
accident greatly accelerated the practice of providing living
accommodations on separate platforms, away from those used for
extraction.

However, this was in itself a hazardous environment. In March
1980, the 'flotel' (floating
hotel) platform Alexander
Kjelland capsized in a storm in the North Sea with the loss of 123 lives.[5]

Given the number of grievances and conspiracy theories that
involve the oil business, and the importance of gas/oil platforms
to the economy, platforms in the United States are believed to be
potential terrorist targets. Agencies and military units
responsible for maritime counterterrorism in the US (Coast Guard, Navy
SEALs, Marine
Recon) often train for platform raids.

Ecological
effects

NOAA map of the 3,858 oil and gas platforms extant in the Gulf of
Mexico in 2006

In British waters, the cost of removing all platform rig
structures entirely was estimated in 1995 at £1.5 billion, and the
cost of removing all structures including pipelines — a so-called
"clean sea" approach — at £3 billion.

Further effects are the leaching of heavy metals that
accumulate in buoyancy tanks into water; and risks associated with
their disposal. There has been concern expressed at the practice of
partially demolishing offshore rigs to the point that ships can
traverse across their site; there have been instances of fishery vessels snagging nets
on the remaining structures. Proposals for the disposal at sea of
the Brent Spar, a
449 ft (137 m) tall storage buoy (another true function
of that which is termed an oil rig), was for a time in 1996 an
environmental cause célèbre in the UK after Greenpeace occupied the
floating structure. The event led to a reconsideration of disposal
policy in the UK and Europe.

In the United States, Marine Biologist Milton Love has proposed
that oil platforms off the California coast be retained as artificial
reefs, instead of being dismantled (at great cost), because he
has found them to be havens for many of the species of fish which
are otherwise declining in the region, in the course of 11 years of
research.[6] Love is
funded mainly by government agencies, but also in small part by the
California Artificial Reef Enhancement Program. NOAA has said it is
considering this course of action, but wants money to study the
effects of the rigs in detail. Divers have been used to assess the
fish populations surrounding the
platforms.[7] In the
Gulf of
Mexico, more than 200 platforms have been similarly
converted.

An oil platform is a large structure placed in the sea. It is used to drill for oil or natural gas at the bottom of the sea. The platform may be attached to the sea floor (stationary)or it might be movable(mobile).

In general, oil platforms are located on the continental shelf. As of 2006, drilling for resources up to 8km away from the platform was possible.